research

EXPERTS

Christopher Kucharik
Professor
Agronomy, Nelson Institute Center for Sustainability and the Global Environment

Stephen Carpenter
Director, Center for Limnology and
Stephen Alfred Forbes Professor of Zoology

Eric Booth
Assistant Research Scientist
Agronomy and Civil & Environmental Engineering

Xi Chen
Postdoctoral Researcher

Melissa Motew
Environment & Resources, PhD

Chloe Wardropper
Environment & Resources, PhD

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Agriculture in the Yahara Watershed

water quality

The Yahara lakes are among the world’s most studied bodies of freshwater. Changes in climate and land use are impacting their health and could continue to do so into the future. An impact of particular concern is phosphorus pollution from agricultural and urban areas.

While essential for life, phosphorus is harmful when in excess in soil and water. Erosion and surface runoff transport phosphorus from farmland and urban areas into the lakes, which results in eutrophication, or a surplus of nutrients in the water. Algal blooms are the most visible sign of eutrophication and are a frequent occurrence in the Yahara lakes in the summer. They disrupt natural ecological processes in freshwater and can be harmful to animals and humans.

Our water quality research improves our understanding of how current and future climate and land-use changes could affect phosphorus pollution levels and subsequent lake health, pointing to ways we could improve water quality in the region and beyond.

What we asked

How have changes in climate, land use, and land management affected lake water quality over the past several decades? What has been the effect of water quality initiatives over this time period, including the adoption of agricultural best management practices (BMPs)?
What could lake water quality be like in the year 2070 under certain conditions of social and environmental change, especially those outlined in the Yahara 2070 scenarios?
How would different phosphorus management strategies affect lake water quality under future climate change?

What we found

Despite significant efforts to improve lake water quality in the last several decades, several factors have resulted in no significant change in the amount of phosphorus entering the lakes. Our research shows more frequent heavy rain events, urban expansion, larger livestock herds on smaller parcels of land, and more row crops have hindered progress. Addressing these factors will be critical for reducing phosphorus loads and improving water quality. That said, beneficial factors such as better farming practices, urban runoff management, improved cow diets, and decreased fertilizer use are helping and may be the reason lake water quality has not gotten worse.
Our research shows a powerful determinant of water quality is legacy phosphorus, or the buildup of phosphorus in soils, streams, wetlands, and lakes from historical land management practices. To improve water quality, it will be necessary to develop and implement practices that reduce the amount of legacy phosphorous stored in the watershed’s soils, in addition to continuing practices that reduce the transport of phosphorus from land to water, such as stream buffers.
Substantial land-use changes such as those that occur in the Yahara 2070 scenarios - for example, more grass grown for biofuels and the elimination of manure - could improve lake water clarity by one foot, as measured by a secchi disk, by 2070.
Even with significant land-use changes, aquatic invasive species could be game changers in efforts to clean up the lakes. Invasive species like the spiny water flea, which is already established in Lake Mendota, could make it more difficult to improve water quality, because they eat Daphnia, a zooplankton that eats algae. Protecting Daphnia and preventing or controlling invasive species will be critical to continue making progress.